Pliers of this kind are also called crimping pliers or pressing pliers. Depending on the design of the work piece, especially in case of fittings, tubes and the like to be crimped, substantial pressing forces have to be applied onto the work piece. On the other hand, such work pieces may have comparatively great dimensions. Consequently, the crimping die being formed by two dies should have a great opening in the opened position of the pliers to be able to move the two dies over the work piece to be crimped in the opened position of the pliers. At the beginning of the closing movement of the pliers, there usually are no or no substantial pressing forces to be overcome. Contrarily, the pressing forces to be applied during the actual crimping movement of the work piece are substantial.
Pliers for crimping work pieces are known from German patent application DE 197 09 639 Al. The pliers include two handles being movable with respect to one another by one hand. Two pivot jaws are supported by a joint. One of the pivot jaws is connected to a stationary handle to form a stationary portion of the pliers. The other pivot jaw is pivotally connected to the stationary portion of the pliers by the joint. The pliers include separated dies forming a crimping die. A locking mechanism serves to reach a defined end position of the separated dies. The handles many first be reopened after the crimping process has been finished, after the end position has been reached and after the locking mechanism has released the handles. A pressure lever is arranged between the handles, and it is pivotable by the supporting joint. The pressure lever together with a section of the movable handle forms a toggle lever drive. The two dies and the corresponding pivot jaws are designed as one piece. The fixed connection of the combined pivot jaw/die to the stationary handle is disadvantageous. The maximum appliable crimping forces are limited. Additionally, the preciseness of the finished crimped work piece highly depends on the realizable process tolerances with which the elements of the pliers are produced and which are used to assemble the pliers. Consequently, in many cases it is necessary to rework the pliers. The known pliers include handles made of molded plastic. These handles provide great stability at reduced exactness. Since the material flows, disadvantageous displacements of, for example, prearrange bores cannot be prevented. The work piece is crimped in one crimping step.
Pliers for producing solderless connections between current conduits and corresponding connection elements by crimping the work pieces are known from German Auslegeschrift DE-AS 21 49 167. The pliers have a plate design, and they provide the corresponding advantages. The rather simple and exact production of the plates, for example by punching, is advantageous.
Linearly driven pliers having a plate design are also known from German patent 34 11 397 C2. The necessary forces for producing solderless connections are not substantial.
Clamping pliers are known from German patent DE 25 59 656 B2. The clamping pliers include two handles being movable with respect to one another. Two pivot jaws are rotatable about a common joint. One of the pivot jaws is connected to a fixed handle to form a fixed pliers portion. The other pivot jaw is pivotally connected to the fixed pliers portion by the joint. A pressure lever is arranged between the two handles. The pressure lever is pivotal about a supporting joint and, together with a section of the fixed handle, it forms a toggle lever drive. To adjust the effective length of the pressure lever despite the fixed connection of the pressure lever at both ends at the handles, at least one of the supporting joints includes an eccentric tappet including different angle positions to adjust the kinematics of the clamping pliers, especially of the end position during the closing movement of the pivot jaws.
German patent DE 25 55 071 C2 additionally shows the application of a locking mechanism being arranged between the pressure lever and the fixed handle to reproducibly attain the defined end position.
A crimping die including two handles being movable with respect to one another and two pivot jaws being pivotal about a common joint are known from US. Pat. No. 3,324,702. One of the pivot jaws includes a die. The other pivot jaw is connected to the fixed handle to form a fixed pliers portion. The closing movement between the two handles is separated into a majority of crimping processes without a defined end position by a jack drive. Two pressure levers are arranged between the two handles to be pivotal about two additional supporting joints and by one common connecting joint. The jack drive or the ratchet drive includes a cam disk contacting a roller being supported at the connecting joint. In this way, a toggle lever drive is realized between the pivot jaws. Due to the fact that a jack drive is used, there is no locking mechanism for attaining a defined end position during the closing movement.